Q fever and Coxiella burnetii: a model for host-parasite interactions

Molecular identification of tick (Acari: Ixodidae) and tick-borne pathogens from Przewalski's gazelle (Procapra Przewalskii) and Tibetan sheep (Ovis aries) in Qinghai Lake National Nature Reserve, China

The Qinghai Lake National Nature Reserve (QLNNR), renowned for its abundant natural resources and diverse ecological habitats, serves as an ideal environment for ticks, thereby increasing the risk of various tick-borne pathogens (TBPs) transmission. This study aimed to investigate the prevalence of TBPs in ticks collected from Przewalski's gazelle and Tibetan sheep within the QLNNR. A total of 313 tick samples were collected from the vicinity of Qinghai Lake. Tick species identification was conducted using both morphological and molecular biology techniques. Polymerase chain reaction (PCR) amplification was performed to detect the presence of spotted fever group (SFG) Rickettsia, Coxiella burnetii, Anaplasma phagocytophilum, Babesia microti, Theileria spp, Borrelia burgdorferi, Brucella spp, and Anaplasma ovis was performed using specific primers. Positive samples were sequenced and analyzed using BLASTn, followed by phylogenetic tree construction. The ticks collected from the Qinghai Lake area were identified as Dermacentor nuttalli. The overall prevalence rates of ticks carrying SFG Rickettsia and C. burnetii were 42.8 % (134/313) and 4.8 % (15/313), respectively. Three SFG Rickettsia species were detected, including R. raoultii 33.9 % (106/313), R. slovaca 3.8 % (12/113) and R. sibirica 7.7 % (24/113), with R. raoultii being the predominant species. The prevalence rates of SFG Rickettsia and C. burnetii in ticks from Tibetan sheep was 44.7 % (115/257) and 4.7 % (12/257), respectively,and in ticks from Przewalski's gazelle were 33.9 % (19/56) and 5.4 % (3/56). Furthermore, the study revealed a positive linear relationship between the abundance of Przewalski's gazelle and the number of ticks, as well as the prevalence of TBPs. The current study has identified Dermacentor nuttalli as the predominant tick vector species within the QLNNR region. The detection of SFG Rickettsia and C. burnetii has augmented our understanding of the epidemiological profile of ticks and TBPs in this area, thereby providing a robust theoretical foundation for the implementation of effective prevention and control strategies against TBPs.

Molecular and genotyping techniques in diagnosis of Coxiella burnetii: An overview

Although we live in the genomic era, the accessibility of the complete genome sequence of Coxiella burnetii, the etiological agent of Q fever, has increased knowledge in the field of genomic diversity of this agent However, it is still somewhat of a "question" microorganism. The epidemiology of Q fever is intricate due to its global distribution, repository and vector variety, as well as absence of surveys defining the dynamic interaction among these factors. Moreover, C. burnetii is a microbial agent that can be utilized as a bioterror weapon. Therefore, typing techniques used to recognize the strains can also be used to trace infections back to their source which is of great significance. In this paper, the latest and current typing techniques of C. burnetii spp. are reviewed illustrating their advantages and constraints. Recently developed multi locus VNTR analysis (MLVA) and single-nucleotide polymorphism (SNP) typing methods are promising in improving diagnostic capacity and enhancing the application of genotyping techniques for molecular epidemiologic surveys of the challenging pathogen. However, most of these studies did not differentiate between C. burnetii and Coxiella-like endosymbionts making it difficult to estimate the potential role that ticks play in the epidemiology of Q fever. Therefore, it is necessary to analyze the vector competence of different tick species to transmit C. burnetii. Knowledge of the vector and reservoir competence of ticks is important for taking adequate preventive measures to limit infection risks. The significant prevalence observed for the IS1111 gene underscores its substantial presence, while other genes display comparatively lower prevalence rates. Methodological variations, particularly between commercial and non-commercial kit-based methods, result in different prevalence outcomes. Variations in sample processing procedures also lead to significant differences in prevalence rates between mechanical and non-mechanical techniques.

The inside scoop: Comparative genomics of two intranuclear bacteria, "Candidatus Berkiella cookevillensis" and "Candidatus Berkiella aquae"

"Candidatus Berkiella cookevillensis" (strain CC99) and "Candidatus Berkiella aquae" (strain HT99), belonging to the Coxiellaceae family, are gram-negative bacteria isolated from amoebae in biofilms present in human-constructed water systems. Both bacteria are obligately intracellular, requiring host cells for growth and replication. The intracellular bacteria-containing vacuoles of both bacteria closely associate with or enter the nuclei of their host cells. In this study, we analyzed the genome sequences of CC99 and HT99 to better understand their biology and intracellular lifestyles. The CC99 genome has a size of 2.9Mb (37.9% GC) and contains 2,651 protein-encoding genes (PEGs) while the HT99 genome has a size of 3.6Mb (39.4% GC) and contains 3,238 PEGs. Both bacteria encode high proportions of hypothetical proteins (CC99: 46.5%; HT99: 51.3%). The central metabolic pathways of both bacteria appear largely intact. Genes for enzymes involved in the glycolytic pathway, the non-oxidative branch of the phosphate pathway, the tricarboxylic acid pathway, and the respiratory chain were present. Both bacteria, however, are missing genes for the synthesis of several amino acids, suggesting reliance on their host for amino acids and intermediates. Genes for type I and type IV (dot/icm) secretion systems as well as type IV pili were identified in both bacteria. Moreover, both bacteria contain genes encoding large numbers of putative effector proteins, including several with eukaryotic-like domains such as, ankyrin repeats, tetratricopeptide repeats, and leucine-rich repeats, characteristic of other intracellular bacteria.

Detection of Ticks and Tick-Borne Pathogens of Urban Stray Dogs in South Africa

This study aimed to identify ticks infesting dogs admitted to the Potchefstroom Animal Welfare Society (PAWS) and to detect tick-borne pathogens they are harbouring. A total of 592 ticks were collected from 61 stray dogs admitted to PAWS originating from several suburbs in and near Potchefstroom, South Africa. The dog ticks were identified as Haemaphysalis elliptica (39%) and Rhipicephalus sanguineus (61%) by both morphological and DNA analyses. Of these ticks, H. elliptica consisted of 67.5% (156/231) and 32.5% (75/231) female and male ticks, respectively, whilst R. sanguineus consisted of 48.5% (175/361) and 51.5% (186/361) female and male ticks, respectively. Microscopic examination of blood smears from engorged female ticks indicated overall occurrences of 0.5% (1/204) for Babesia spp. from R. sanguineus, 1% (2/204) of Anaplasma spp. from H. elliptica, and 22% (45/204) of Rickettsia spp. from both H. elliptica and R. sanguineus. Using pooled samples molecular detection of tick-borne pathogens indicated overall occurrences of 1% (1/104) for A. phagocytophilum in H. elliptica, 9.6% (10/104) of Rickettsia spp. in H. elliptica and R. sanguineus, 5.8% (6/104) of Ehrlichia canis in H. elliptica and R. sanguineus, and 13.5% (14/104) of Coxiella spp. in both H. elliptica and R. sanguineus. Additionally, PCR detected 6.5% (2/31) of Coxiella spp. DNA from H. elliptica eggs. Our data indicate that urban stray dogs admitted at PAWS are infested by H. elliptica and R. sanguineus ticks which are harbouring several pathogenic organisms known to cause tick-borne diseases.

Inactivation Kinetics of Coxiella burnetii During High-Temperature Short-Time Pasteurization of Milk

The Gram-negative, obligate intracellular bacterium Coxiella burnetii is the causative organism of the zoonosis Q fever and is known for its resistance toward various intra- and extracellular stressors. Infected ruminants such as cattle, sheep, and goats can shed the pathogen in their milk. Pasteurization of raw milk was introduced for the inactivation of C. burnetii and other milk-borne pathogens. Legal regulations for the pasteurization of milk are mostly based on recommendations of the Codex Alimentarius. As described there, C. burnetii is considered as the most heat-resistant non-spore-forming bacterial pathogen in milk and has to be reduced by at least 5 log10-steps during the pasteurization process. However, the corresponding inactivation data for C. burnetii originate from experiments performed more than 60 years ago. Recent scientific findings and the technological progress of modern pasteurization equipment indicate that C. burnetii is potentially more effectively inactivated during pasteurization than demanded in the Codex Alimentarius. In the present study, ultra-high heat-treated milk was inoculated with different C. burnetii field isolates and subsequently heat-treated in a pilot-plant pasteurizer. Kinetic inactivation data in terms of D- and z-values were determined and used for the calculation of heat-dependent log reduction. With regard to the mandatory 5 log10-step reduction of the pathogen, the efficacy of the established heat treatment regime was confirmed, and, in addition, a reduction of the pasteurization temperature seems feasible.

Critical Role for Molecular Iron in Coxiella burnetii Replication and Viability

Coxiella burnetii, the causative agent of Query (Q) fever in humans, is a highly infectious obligate intracellular bacterium. Following uptake into a host cell, C. burnetii replicates within a phagolysosome-derived compartment referred to as the Coxiella-containing vacuole (CCV). During infection, C. burnetii exhibits tropism for tissues related to iron storage and recycling (e.g., the liver and splenic red pulp), suggesting that pathogen physiology is linked to host iron metabolism. Iron has been described to have a limited role in C. burnetii virulence regulation, despite evidence that C. burnetii -infected host cells increase expression of transferrin receptors, thereby suggesting that active iron acquisition by the bacterium occurs upon infection. Through the use of host cell-free culture, C. burnetii was separated from the host cell in order to directly assess the role of different forms of iron in C. burnetii replication and viability, and therefore virulence. Results indicate that C. burnetii tolerates molecular iron over a broad concentration range (i.e., ∼0.001 to 1 mM) and undergoes gross loss of viability upon iron starvation. C. burnetii protein synthesis and energy metabolism, however, occur nearly uninhibited under iron concentrations not permissive to replication. Despite the apparent absence of genes related to acquisition of host-associated iron-containing proteins, C. burnetii replication is supported by hemoglobin, transferrin, and ferritin, likely due to release of iron from such proteins under acidic conditions. Moreover, chelation of host iron pools inhibited pathogen replication during infection of cultured cells.IMPORTANCE Host organisms restrict the availability of iron to invading pathogens in order to reduce pathogen replication. To counteract the host's response to infection, bacteria can rely on redundant mechanisms to obtain biologically diverse forms of iron during infection. C. burnetii appears specifically dependent on molecular iron for replication and viability and exhibits a response to iron akin to bacteria that colonize iron-rich environments. Physiological adaptation of C. burnetii to the unique acidic and degradative environment of the CCV is consistent with access of this pathogen to molecular iron.

Major Histocompatibility Complex Class II-Restricted, CD4+ T Cell-Dependent and -Independent Mechanisms Are Required for Vaccine-Induced Protective Immunity against Coxiella burnetii

To understand the role of major histocompatibility complex class I (MHC-I) and MHC-II in vaccine-mediated protection against Coxiella burnetii, we evaluated the protective efficacy of a formalin-inactivated C. burnetii Nine Mile phase I vaccine (PIV) in β2-microglobulin-deficient (B2m KO) and MHC-II-deficient (MHC-II KO) mice. Vaccination reduced disease severity in wild-type (WT) and B2m KO mice but failed to reduce bacterial burden in MHC-II KO mice. This suggests that the MHC-II antigen presentation pathway is required for PIV-mediated protection against C. burnetii infection. MHC-I and MHC-II affect antibody isotype switching, since both PIV-vaccinated B2m KO and MHC-II KO mice produced less Coxiella-specific IgG than PIV-vaccinated WT mice. Interestingly, MHC-II and CD4 deficiencies were not equivalent in terms of splenomegaly and bacterial clearance. This demonstrates a partial role for CD4+ T cells while revealing MHC-II-restricted, CD4-independent mechanisms. Adoptive transfer of CD4+ T cells from PIV-vaccinated WT mice to naive CD4-deficient (CD4 KO) mice demonstrated that antigen-experienced CD4+ T cells are sufficient to generate protection. Conversely, transfer of naive CD4+ T cells to PIV-vaccinated CD4 KO mice exacerbates disease. Using Tbet-deficient (Tbet KO) mice, we showed a partial role for Th1 subset CD4+ T cells in vaccine protection. Furthermore, Th1-independent roles for Tbet were suggested by significant differences in disease between PIV-vaccinated Tbet KO and CD4 KO mice. Interferon gamma was shown to contribute to the host inflammatory response but not bacterial clearance. Collectively, these findings suggest that vaccine-induced protective immunity against a murine model of experimental Q fever requires MHC-II-restricted, CD4+ T cell-dependent and -independent mechanisms that can be exploited for a new-generation human Q fever vaccine.

Eosinophils Affect Antibody Isotype Switching and May Partially Contribute to Early Vaccine-Induced Immunity against Coxiella burnetii

Coxiella burnetii is an obligate intracellular Gram-negative bacterium which causes human Q fever. An acidified citrate cysteine medium (ACCM-2) has been developed which mimics the intracellular replicative niche of C. burnetii and allows axenic growth of the bacteria. To determine if C. burnetii cultured in ACCM-2 retains immunogenicity, we compared the protective efficacies of formalin-inactivated C. burnetii Nine Mile phase I (PIV) and phase II (PIIV) vaccines derived from axenic culture 7, 14, and 28 days postvaccination. PIV conferred significant protection against virulent C. burnetii as early as 7 days postvaccination, which suggests that ACCM-2-derived PIV retains immunogenicity and protectivity. We analyzed the cellular immune response in spleens from PIV- and PIIV-vaccinated mice by flow cytometry at 7 and 14 days postvaccination and found significantly more granulocytes in PIV-vaccinated mice than in PIIV-vaccinated mice. Interestingly, we found these infiltrating granulocytes to be SSChigh CD11b+ CD125+ Siglec-F+ (where SSChigh indicates a high side scatter phenotype) eosinophils. There was no change in the number of eosinophils in PIV-vaccinated CD4-deficient mice compared to the level in controls, which suggests that eosinophil accumulation is CD4+ T cell dependent. To evaluate the importance of eosinophils in PIV-mediated protection, we vaccinated and challenged eosinophil-deficient ΔdblGATA mice. ΔdblGATA mice had significantly worse disease than their wild-type counterparts when challenged 7 days postvaccination, while no significant difference was seen at 28 days postvaccination. Nevertheless, ΔdblGATA mice had elevated serum IgM with decreased IgG1 and IgG2a whether mice were challenged at 7 or 28 days postvaccination. These results suggest that eosinophils may play a role in early vaccine protection against C. burnetii and contribute to antibody isotype switching.

Health and zoonotic Infections of snow leopards Panthera unica in the South Gobi desert of Mongolia

Background: Snow leopards, Panthera uncia, are a threatened apex predator, scattered across the mountains of Central and South Asia. Disease threats to wild snow leopards have not been investigated.Methods and Results: Between 2008 and 2015, twenty snow leopards in the South Gobi desert of Mongolia were captured and immobilised for health screening and radio-collaring. Blood samples and external parasites were collected for pathogen analyses using enzyme-linked immunosorbent assay (ELISA), microscopic agglutination test (MAT), and next-generation sequencing (NGS) techniques. The animals showed no clinical signs of disease, however, serum antibodies to significant zoonotic pathogens were detected. These pathogens included, Coxiella burnetii, (25% prevalence), Leptospira spp., (20%), and Toxoplasma gondii (20%). Ticks collected from snow leopards contained potentially zoonotic bacteria from the genera Bacillus, Bacteroides, Campylobacter, Coxiella, Rickettsia, Staphylococcus and Streptococcus.Conclusions: The zoonotic pathogens identified in this study, in the short-term did not appear to cause illness in the snow leopards, but have caused illness in other wild felids. Therefore, surveillance for pathogens should be implemented to monitor for potential longer- term disease impacts on this snow leopard population.

Benefits of a Bacillus probiotic to larval fish survival and transport stress resistance

The need for sustainable bacterial management approaches in aquaculture is crucial for advancement of the industry. Probiotics are a promising strategy as evidenced by benefits demonstrated in intensive larviculture of various marine fish species. In this study we investigate the effects of a mixed Bacillus species (B. licheniformis and B. amyloliquefaciens) probiotic on rearing of larval common snook (Centropomus undecimalis). Experimental treatments included (1) probiotics supplemented to the water and live feed, (2) probiotics supplemented to the water only, and (3) no probiotic controls. Data from two separate trials indicated up to 2.5 times higher survival with probiotic addition, as well as 20% higher survival 7 days following a transport event. These benefits were not explained by faster growth, measured water quality parameters, or innate immune enzyme activities. Microbiota analysis indicated the importance of system stabilization prior to larval stocking to improve rearing success and probiotic performance. ied Potential probiotic benefits include accelerated gastrointestinal tract development, enhanced immunity, inhibition of opportunistic bacteria, and improvements to water quality parameters. Results suggest this probiotic should be tested in other marine fish species in order to reduce larval rearing bottlenecks.

The role of microtubules and the dynein/dynactin motor complex of host cells in the biogenesis of the Coxiella burnetii-containing vacuole

Microtubules (Mts) are dynamic cytoskeleton structures that play a key role in vesicular transport. The Mts-mediated transport depends on motor proteins named kinesins and the dynein/dynactin motor complex. The Rab7 adapter protein FYCO1 controls the anterograde transport of the endocytic compartments through the interaction with the kinesin KIF5. Rab7 and its partner RILP induce the recruitment of dynein/dynactin to late endosomes regulating its retrograde transport to the perinuclear area to fuse with lysosomes. The late endosomal-lysosomal fusion is regulated by the HOPS complex through its interaction with RILP and the GTPase Arl8. Coxiella burnetii (Cb), the causative agent of Q fever, is an obligate intracellular pathogen, which generates a large compartment with autophagolysosomal characteristics named Cb-containing vacuole (CCV). The CCV forms through homotypic fusion between small non-replicative CCVs (nrCCV) and through heterotypic fusion with other compartments, such as endosomes and lysosomes. In this work, we characterise the role of Mts, motor proteins, RILP/Rab7 and Arl8 on the CCV biogenesis. The formation of the CCV was affected when either the dynamics and/or the acetylation state of Mts were modified. Similarly, the overexpression of the dynactin subunit non-functional mutants p150^Glued and RILP led to the formation of small nrCCVs. This phenomenon is not observed in cells overexpressing WT proteins, the motor KIF5 or its interacting protein FYCO1. The formation of the CCV was normal in infected cells that overexpressed Arl8 alone or together with hVps41 (a HOPS subunit) or in cells co-overexpressing hVps41 and RILP. The dominant negative mutant of Arl8 and the non-functional hVps41 inhibited the formation of the CCV. When the formation of CCV was affected, the bacterial multiplication diminished. Our results suggest that nrCCVs recruit the molecular machinery that regulate the Mts-dependent retrograde transport, Rab7/RILP and the dynein/dynactin system, as well as the tethering processes such as HOPS complex and Arl8 to finally originate the CCV where C. burnetii multiplies.

Screening for Q fever. A tertiary care hospital-based experience in central Saudi Arabia

OBJECTIVES

To evaluate the presence of Coxiella burnetii  (C. brunetii) infection among patients presenting with fever of unknown origin (FUO).

METHODS

A cross-sectional study of 100 patients (54 men and 46 women; mean age: 34.3 ± 19.2 years) with FUO was conducted at King Khalid University Hospital, Riyadh, Saudi Arabia between March 2015 and June 2016. Phase 1 and phase 2 C. burnetii-specific antibodies in serum samples were detected by enzyme-linked immunosorbent assay.

RESULTS

Coxiella burnetii phase 1 and phase 2 antibodies were detected in 16% of the patients. Phase 2 IgM was present in 2% of the patients, whereas phase 2 IgG antibodies were detected in 11%  of the patients. Coxiella burnetii-specific phase 1 IgG was found in 2% of the patients, and 8% of the patients harbored phase 1 IgA antibodies in their serum.

CONCLUSION

The presence of C. burnetii-specific antibodies in many patients suffering from FUO highlights the importance of Q fever screening among patients presenting with febrile illness.

Detecting Biothreat Agents: From Current Diagnostics to Developing Sensor Technologies

Although a fundamental understanding of the pathogenicity of most biothreat agents has been elucidated and available treatments have increased substantially over the past decades, they still represent a significant public health threat in this age of (bio)terrorism, indiscriminate warfare, pollution, climate change, unchecked population growth, and globalization. The key step to almost all prevention, protection, prophylaxis, post-exposure treatment, and mitigation of any bioagent is early detection. Here, we review available methods for detecting bioagents including pathogenic bacteria and viruses along with their toxins. An introduction placing this subject in the historical context of previous naturally occurring outbreaks and efforts to weaponize selected agents is first provided along with definitions and relevant considerations. An overview of the detection technologies that find use in this endeavor along with how they provide data or transduce signal within a sensing configuration follows. Current "gold" standards for biothreat detection/diagnostics along with a listing of relevant FDA approved in vitro diagnostic devices is then discussed to provide an overview of the current state of the art. Given the 2014 outbreak of Ebola virus in Western Africa and the recent 2016 spread of Zika virus in the Americas, discussion of what constitutes a public health emergency and how new in vitro diagnostic devices are authorized for emergency use in the U.S. are also included. The majority of the Review is then subdivided around the sensing of bacterial, viral, and toxin biothreats with each including an overview of the major agents in that class, a detailed cross-section of different sensing methods in development based on assay format or analytical technique, and some discussion of related microfluidic lab-on-a-chip/point-of-care devices. Finally, an outlook is given on how this field will develop from the perspective of the biosensing technology itself and the new emerging threats they may face.

On the possible role of ticks in the eco-epidemiology of Coxiella burnetii in a Mediterranean ecosystem

Ruminant livestock is the main reservoir of Coxiella burnetii (Cb), but little is known about the role of wildlife and ticks in its epidemiology. The Iberian ibex (Capra pyrenaica, Schinz 1838) population of "Ports de Tortosa i Beseit" (NE Spain) suffers intense tick infestations and low reproduction rates. This study aims to (1) assess the relationship between infection in ibexes (detection of serum antibodies and/or of Cb DNA in tissues) and Cb DNA presence in ticks hosted by the same ibexes; and (2) identify Cb associated risk factors. Between 2011 and 2015, serum (n = 130), spleen (n = 72), lymph node (n = 89) and tick (n = 669) samples from 134 hunter-harvested ibexes were collected. Antibody detection was performed by ELISA and Cb DNA presence was assessed by PCR. Potential risk factors were assessed with regression tree models. Although 30% of the ibexes (39/130; 95%CI, [10%-29.8%]) had antibodies, Cb DNA was detected in only 9.8% of the ibexes (11/112; 95%CI [7.6%-27.25%]). The prevalence of Cb-carrier ticks averaged 10% and exceeded 20% for the genus Haemaphysalis. However, lacking correlation between infection in ibexes and their ticks does not support tick-to-ibex transmission or vice versa. Tree modelling points to host, population and environmental factors as drivers of Cb infection in ticks and suggests connections with the domestic cycle. The percentage of Cb-carrier ticks detected is noteworthy. Along with heavy tick infestations, it suggests vector potential for these tick species, especially for the genera Rhipicephalus and Haemaphysalis. Since vector competence has not been assessed in these tick species, a classic vector role cannot be proposed nor discarded, but promoter factors of vector capacity occur. In addition, the risk of tick-borne infection through tick excreta should not be neglected. While the airborne route is the preeminent route for Cb infection, ticks' contribution to Cb epidemiology deserves further attention.

A human time dose response model for Q fever

The causative agent of Q fever, Coxiella burnetii, has the potential to be developed for use in biological warfare and it is classified as a bioterrorism threat agent by the Centers for Disease Control and Prevention (CDC) and as a category B select agent by the National Institute of Allergy and Infectious Diseases (NIAID). In this paper we focus on the in-host properties that arise when an individual inhales a dose of C. burnetii and establish a human time-dose response model. We also propagate uncertainty throughout the model allowing us to robustly estimate key properties including the infectious dose and incubation period. Using human study data conducted in the 1950's we conclude that the dose required for a 50% probability of infection is about 15 organisms, and that one inhaled organism of C. burnetti can cause infection in 5% of the exposed population. In addition, we derive a low dose incubation period of 17.6 days and an extracellular doubling time of half a day. In conclusion this paper provides a framework for detailing the parameters and approaches that would be required for risk assessments associated with exposures to C. burnetii that might cause human infection.

Phase variation of Coxiella burneti0i strain Priscilla: influence of this phenomenon on biochemical features of its lipopolysaccharide

During the phase variation of Coxiella burnetii, modifications in its lipopolysaccharide (LPS) component were investigated. The cloned phase I C. burnetii cells were passed serially in chicken embryo yolk sacs up to the egg passage (EP) 90. The LPSs from the cells in EPs 3, 12, 21, 40, 60, and 90 were all separated by steric exclusion chromatography into three major populations: the high, intermediate, and low molecular weight fractions, differing one from another in size and chemical composition. No noticeable shortening of the O-polysaccharide chains was observed in the LPSs isolated during the C. burnetii cultivation. However, a redistribution of the existing LPS populations has been observed due to an increasing prevalence of those cells in the whole cell population that express LPS molecules with truncated O-chains and those being of R-type. In the high and intermediate molecular weight LPS populations, virenose and dihydrohydroxystreptose are lost gradually with the progress in phase variation. This occurs more readily with the former sugar. At present, the molecular mechanisms influencing the LPS modifications during the C. burnetii phase variation remain unclear.

The inhibition of the apoptosis pathway by the Coxiella burnetii effector protein CaeA requires the EK repetition motif, but is independent of survivin

ABSRTACT Coxiella burnetii is an obligate intracellular bacterium that causes Query (Q) fever, a zoonotic disease. It requires a functional type IV secretion system (T4SS) which translocate bacterial effector proteins into the host cell cytoplasm and thereby facilitates bacterial replication. To date, more than 130 effector proteins have been identified, but their functions remain largely unknown. Recently, we demonstrated that one of these proteins, CaeA (CBU1524) localized to the host cell nucleus and inhibited intrinsic apoptosis of HEK293 or CHO cells. In the present study we addressed the question whether CaeA also affects the extrinsic apoptosis pathway. Ectopic expression of CaeA reduced extrinsic apoptosis and prevented the cleavage of the executioner caspase 7, but did not impair the activation of initiator caspase 9. CaeA expression resulted in an up-regulation of survivin (an inhibitor of activated caspases), which, however, was not causal for the anti-apoptotic effect of CaeA. Comparing the sequence of CaeA from 25 different C. burnetii isolates we identified an EK (glutamic acid/ lysine) repetition motif as a site of high genetic variability. The EK motif of CaeA was essential for the anti-apoptotic activity of CaeA. From these data, we conclude that the C. burnetii effector protein CaeA interferes with the intrinsic and extrinsic apoptosis pathway. The process requires the EK repetition motif of CaeA, but is independent of the upregulated expression of survivin.

Coxiella burnetii Phagocytosis Is Regulated by GTPases of the Rho Family and the RhoA Effectors mDia1 and ROCK

The GTPases belonging to the Rho family control the actin cytoskeleton rearrangements needed for particle internalization during phagocytosis. ROCK and mDia1 are downstream effectors of RhoA, a GTPase involved in that process. Coxiella burnetii, the etiologic agent of Q fever, is internalized by the host´s cells in an actin-dependent manner. Nevertheless, the molecular mechanism involved in this process has been poorly characterized. This work analyzes the role of different GTPases of the Rho family and some downstream effectors in the internalization of C. burnetii by phagocytic and non-phagocytic cells. The internalization of C. burnetii into HeLa and RAW cells was significantly inhibited when the cells were treated with Clostridium difficile Toxin B which irreversibly inactivates members of the Rho family. In addition, the internalization was reduced in HeLa cells that overexpressed the dominant negative mutants of RhoA, Rac1 or Cdc42 or that were knocked down for the Rho GTPases. The pharmacological inhibition or the knocking down of ROCK diminished bacterium internalization. Moreover, C. burnetii was less efficiently internalized in HeLa cells overexpressing mDia1-N1, a dominant negative mutant of mDia1, while the overexpression of the constitutively active mutant mDia1-ΔN3 increased bacteria uptake. Interestingly, when HeLa and RAW cells were infected, RhoA, Rac1 and mDia1 were recruited to membrane cell fractions. Our results suggest that the GTPases of the Rho family play an important role in C. burnetii phagocytosis in both HeLa and RAW cells. Additionally, we present evidence that ROCK and mDia1, which are downstream effectors of RhoA, are involved in that process.

Role of B cells in host defense against primary Coxiella burnetii infection

Despite Coxiella burnetii being an obligate intracellular bacterial pathogen, our recent study demonstrated that B cells play a critical role in vaccine-induced immunity to C. burnetii infection by producing protective antibodies. However, the role of B cells in host defense against primary C. burnetii infection remains unclear. In this study, we investigated whether B cells play an important role in host defense against primary C. burnetii infection. The results showed that peritoneal B cells were able to phagocytose virulent C. burnetii bacteria and form Coxiella-containing vacuoles (CCVs) and that C. burnetii can infect and replicate in peritoneal B1a subset B cells in vitro, demonstrating a potential role for peritoneal B cells in host defense against C. burnetii infection in vivo. In addition, the results showing that B1a cells secreted a high level of interleukin-10 (IL-10) in response to C. burnetii infection in vitro suggest that B1a cells may play an important role in inhibiting the C. burnetii infection-induced inflammatory response. The observation that adoptive transfer of peritoneal B cells did not significantly affect the severity of C. burnetii infection-induced diseases in both severe combined immunity-deficient (SCID) and μMT mice indicates that peritoneal B cells alone may not be able to control C. burnetii infection. In contrast, our finding that C. burnetii infection induced more-severe splenomegaly and a higher bacterial burden in the spleens of B1a cell-deficient Bruton's tyrosine kinase x-linked immunity-deficient (BTK(xid)) mice than in their wild-type counterparts further suggests that B1a cells play an important role in host defense against primary C. burnetii infection.

Chloroform-Methanol Residue of Coxiella burnetii Markedly Potentiated the Specific Immunoprotection Elicited by a Recombinant Protein Fragment rOmpB-4 Derived from Outer Membrane Protein B of Rickettsia rickettsii in C3H/HeN Mice

The obligate intracellular bacteria, Rickettsia rickettsii and Coxiella burnetii, are the potential agents of bio-warfare/bio-terrorism. Here C3H/HeN mice were immunized with a recombinant protein fragment rOmp-4 derived from outer membrane protein B, a major protective antigen of R. rickettsii, combined with chloroform-methanol residue (CMR) extracted from phase I C. burnetii organisms, a safer Q fever vaccine. These immunized mice had significantly higher levels of IgG1 and IgG2a to rOmpB-4 and interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α), two crucial cytokines in resisting intracellular bacterial infection, as well as significantly lower rickettsial loads and slighter pathological lesions in organs after challenge with R. rickettsii, compared with mice immunized with rOmpB-4 or CMR alone. Additionally, after challenge with C. burnetii, the coxiella loads in the organs of these mice were significantly lower than those of mice immunized with rOmpB-4 alone. Our results prove that CMR could markedly potentiate enhance the rOmpB-4-specific immunoprotection by promoting specific and non-specific immunoresponses and the immunization with the protective antigen of R. rickettsii combined with CMR of C. burnetii could confer effective protection against infection of R. rickettsii or C. burnetii.

Emergence of Coxiella burnetii in ruminants on Reunion Island? Prevalence and risk factors

Q fever is a widespread zoonosis that is caused by Coxiella burnetii (C. burnetii), and ruminants are identified as the main sources of human infections. Some human cases have been described, but very limited information was available about Q fever in ruminants on Reunion Island, a tropical island in the Indian Ocean. A cross-sectional study was undertaken from March 2011 to August 2012 to assess the Q fever prevalence and to identify the major risk factors of C. burnetii infection in ruminants. A total of 516 ruminants (245 cattle, 137 sheep and 134 goats) belonging to 71 farms and localized in different ecosystems of the island were randomly selected. Samples of blood, vaginal mucus and milk were concomitantly collected from females, and a questionnaire was submitted to the farmers. Ticks from positively detected farms were also collected. The overall seropositivity was 11.8% in cattle, 1.4% in sheep and 13.4% in goats. C. burnetii DNA was detected by PCR in 0.81%, 4.4% and 20.1% in cow, sheep and goat vaginal swabs, respectively. C. burnetii shedding in milk was observed in 1% of cows, 0% in sheep and 4.7% in goats. None of the ticks were detected to be positive for C. burnetii. C. burnetii infection increased when the farm was exposed to prevailing winds and when there were no specific precautions for a visitor before entering the farm, and they decreased when a proper quarantine was set up for any introduction of a new ruminant and when the animals returned to the farm at night. MLVA genotyping confirmed the role of these risk factors in infection.

Q fever is a disease that could be transmitted from animals (cattle, sheep and goats) to humans and caused by a bacterium called Coxiella burnetii (C. burnetii). Some human cases exhibiting characteristic clinical signs of that disease have been detected on Reunion Island, a tropical island in the Indian Ocean, but to date, we did not know if these animals could be seen as potential sources of the disease. Thus, a study was undertaken from March 2011 to August 2012 to detect the presence of that bacterium in these animals and to understand how they could get infected themselves. A total of 516 ruminants (245 cattle, 137 sheep and 134 goats) belonging to 71 farms and localized in different environments of the island were selected. Samples of blood, vaginal mucus and milk were concomitantly collected from females, and a questionnaire was submitted to the farmers. Ticks from positively detected farms were also collected. We observed 11.8% of cattle, 1.4% of sheep and 13.4% of goats had already been in contact with the bacterium. Coxiella burnetii was also directly detected in some vaginal and milk samples. None of the ticks were detected to be positive for C. burnetii. We found that the ruminants could be infected when their farm was exposed to prevailing winds because the bacterium can be transported by the wind, and when there were no specific precautions for visitors before entering the farm, because they could act as mechanical carriers of Coxiella. Conversely, keeping new animals under surveillance for some days to detect any signs of the disease before they enter the farm or keeping the animals in the barn at night limit the risk of infection.

Interactions of glycosphingolipids and lipopolysaccharides with silica and polyamide surfaces: adsorption and viscoelastic properties

Bacterial outer membrane components play a critical role in bacteria-surface interactions (adhesion and repulsion). Sphingomonas species (spp.) differ from other Gram-negative bacteria in that they lack lipopolysaccharides (LPSs) in their outer membrane. Instead, Sphingomonas spp. outer membrane consists of glycosphingolipids (GSLs). To delineate the properties of the outer membrane of Sphingomonas spp. and to explain the adhesion of these cells to surfaces, we employed a single-component-based approach of comparing GSL vesicles to LPS vesicles. This is the first study to report the formation of vesicles containing 100% GSL. Significant physicochemical differences between GSL and LPS vesicles are reported. Composition-dependent vesicle adherence to different surfaces using quartz crystal microbalance with dissipation monitoring (QCM-D) technology was observed, where higher GSL content resulted in higher mass accumulation on the sensor. Additionally, the presence of 10% GSL and above was found to promote the relative rigidity of the vesicle obtaining viscoelastic ratio of 30-70% higher than that of pure LPS vesicles.

Erythrocyte and blood antibacterial defense

It is an axiom that blood cellular immunity is provided by leukocytes. As to erythrocytes, it is generally accepted that their main function is respiration. Our research provides objective video and photo evidence regarding erythrocyte bactericidal function. Phase-contrast immersion vital microscopy of the blood of patients with bacteremia was performed, and the process of bacteria entrapping and killing by erythrocytes was shot by means of video camera. Video evidence demonstrates that human erythrocytes take active part in blood bactericidal action and can repeatedly engulf and kill bacteria of different species and size. Erythrocytes are extremely important integral part of human blood cellular immunity.

COMPARED WITH PHAGOCYTIC LEUKOCYTES, THE ERYTHROCYTES

a) are more numerous; b) are able to entrap and kill microorganisms repeatedly without being injured; c) are more resistant to infection and better withstand the attacks of pathogens; d) have longer life span and are produced faster; e) are inauspicious media for proliferation of microbes and do not support replication of chlamidiae, mycoplasmas, rickettsiae, viruses, etc.; and f) are more effective and uncompromised bacterial killers. Blood cellular immunity theory and traditional view regarding the function of erythrocytes in human blood should be revised.

Antiapoptotic activity of Coxiella burnetii effector protein AnkG is controlled by p32-dependent trafficking

Intracellular bacterial pathogens frequently inhibit host cell apoptosis to ensure survival of their host, thereby allowing bacterial propagation. The obligate intracellular pathogen Coxiella burnetii displays antiapoptotic activity which depends on a functional type IV secretion system (T4SS). Accordingly, antiapoptotic T4SS effector proteins, like AnkG, have been identified. AnkG inhibits pathogen-induced apoptosis, possibly by binding to the host cell mitochondrial protein p32 (gC1qR). However, the molecular mechanism of AnkG activity remains unknown. Here, we demonstrate that ectopically expressed AnkG associates with mitochondria and traffics into the nucleus after apoptosis induction, although AnkG lacks a predicted nuclear localization signal. We identified the p32 interaction region in AnkG and constructed an AnkG mutant (AnkGR(22/23S)) unable to bind to p32. By using this mutant, we found that intracellular localization and trafficking of AnkG into the nucleus are dependent on binding to p32. Furthermore, we demonstrated that nuclear localization of AnkG but not binding to p32 is required for apoptosis inhibition. Thus, the antiapoptotic activity of AnkG is controlled by p32-mediated intracellular trafficking, which, in turn, seems to be regulated by host cell processes that sense stress.

Cortactin is involved in the entry of Coxiella burnetii into non-phagocytic cells

BACKGROUND

Cortactin is a key regulator of the actin cytoskeleton and is involved in pathogen-host cell interactions. Numerous pathogens exploit the phagocytic process and actin cytoskeleton to infect host cells. Coxiella burnetii, the etiologic agent of Q fever, is internalized by host cells through a molecular mechanism that is poorly understood.

METHODOLOGY/PRINCIPAL FINDING

Here we analyzed the role of different cortactin motifs in the internalization of C. burnetii by non-phagocytic cells. C. burnetii internalization into HeLa cells was significantly reduced when the cells expressed GFP-cortactin W525K, which carries a mutation in the SH3 domain that renders the protein unable to bind targets such as N-WASP. However, internalization was unaffected when the cells expressed the W22A mutant, which has a mutation in the N-terminal acidic region that destroys the protein's ability to bind and activate Arp2/3. We also determined whether the phosphorylation status of cortactin is important for internalization. Expression of GFP-cortactin 3F, which lacks phosphorylatable tyrosines, significantly increased internalization of C. burnetii, while expression of GFP-cortactin 3D, a phosphotyrosine mimic, did not affect it. In contrast, expression of GFP-cortactin 2A, which lacks phosphorylatable serines, inhibited C. burnetii internalization, while expression of GFP-cortactin SD, a phosphoserine mimic, did not affect it. Interestingly, inhibitors of Src kinase and the MEK-ERK kinase pathway blocked internalization. In fact, both kinases reached maximal activity at 15 min of C. burnetii infection, after which activity decreased to basal levels. Despite the decrease in kinase activity, cortactin phosphorylation at Tyr421 reached a peak at 1 h of infection.

CONCLUSIONS/SIGNIFICANCE

Our results suggest that the SH3 domain of cortactin is implicated in C. burnetii entry into HeLa cells. Furthermore, cortactin phosphorylation at serine and dephosphorylation at tyrosine favor C. burnetii internalization. We present evidence that ERK and Src kinases play a role early in infection by this pathogen.

Coxiella burnetii induces apoptosis during early stage infection via a caspase-independent pathway in human monocytic THP-1 cells

The ability of Coxiella burnetii to modulate host cell death may be a critical factor in disease development. In this study, human monocytic THP-1 cells were used to examine the ability of C. burnetii Nine Mile phase II (NMII) to modulate apoptotic signaling. Typical apoptotic cell morphological changes and DNA fragmentation were detected in NMII infected cells at an early stage of infection. FACS analysis using Annexin-V-PI double staining showed the induction of a significant number of apoptotic cells at an early stage of NMII infection. Double staining of apoptotic cell DNA and intracellular C. burnetii indicates that NMII infected cells undergoing apoptosis. Interestingly, caspase-3 was not cleaved in NMII infected cells and the caspase-inhibitor Z-VAD-fmk did not prevent NMII induced apoptosis. Surprisingly, the caspase-3 downstream substrate PARP was cleaved in NMII infected cells. These results suggest that NMII induces apoptosis during an early stage of infection through a caspase-independent pathway in THP-1 cells. In addition, NMII-infected monocytes were unable to prevent exogenous staurosporine-induced apoptotic death. Western blot analysis indicated that NMII infection induced the translocation of AIF from mitochondria into the nucleus. Cytochrome c release and cytosol-to-mitochondrial translocation of the pore-forming protein Bax in NMII infected cells occurred at 24 h post infection. These data suggest that NMII infection induced caspase-independent apoptosis through a mechanism involving cytochrome c release, cytosol-to-mitochondrial translocation of Bax and nuclear translocation of AIF in THP-1 monocytes. Furthermore, NMII infection increased TNF-α production and neutralization of TNF-α in NMII infected cells partially blocked PARP cleavage, suggesting TNF-α may play a role in the upstream signaling involved in NMII induced apoptosis. Antibiotic inhibition of C. burnetii RNA synthesis blocked NMII infection-induced PARP activation. These results suggest that both intracellular C. burnetii replication and secreted TNF-α contribute to NMII infection-triggered apoptosis during an early stage of infection.

Q Fever: current state of knowledge and perspectives of research of a neglected zoonosis

Q fever is an ubiquitous zoonosis caused by an resistant intracellular bacterium, Coxiella burnetii. In certain areas, Q fever can be a severe public health problem, and awareness of the disease must be promoted worldwide. Nevertheless, knowledge of Coxiella burnetii remains limited to this day. Its resistant (intracellular and environmental) and infectious properties have been poorly investigated. Further understanding of the interactions between the infected host and the bacteria is necessary. Domestic ruminants are considered as the main reservoir of bacteria. Infected animals shed highly infectious organisms in milk, feces, urine, vaginal mucus, and, very importantly, birth products. Inhalation is the main route of infection. Frequently asymptomatic in humans and animals, Q fever can cause acute or chronic infections. Financial consequences of infection can be dramatic at herd level. Vaccination with inactive whole-cell bacteria has been performed and proved effective in humans and animals. However, inactive whole-cell vaccines present several defects. Recombinant vaccines have been developed in experimental conditions and have great potential for the future. Q fever is a challenging disease for scientists as significant further investigations are necessary. Great research opportunities are available to reach a better understanding and thus a better prevention and control of the infection.

Profiling the humoral immune response of acute and chronic Q fever by protein microarray

Antigen profiling using comprehensive protein microarrays is a powerful tool for characterizing the humoral immune response to infectious pathogens. Coxiella burnetii is a CDC category B bioterrorist infectious agent with worldwide distribution. In order to assess the antibody repertoire of acute and chronic Q fever patients we have constructed a protein microarray containing 93% of the proteome of Coxiella burnetii, the causative agent of Q fever. Here we report the profile of the IgG and IgM seroreactivity in 25 acute Q fever patients in longitudinal samples. We found that both early and late time points of infection have a very consistent repertoire of IgM and IgG response, with a limited number of proteins undergoing increasing or decreasing seroreactivity. We also probed a large collection of acute and chronic Q fever patient samples and identified serological markers that can differentiate between the two disease states. In this comparative analysis we confirmed the identity of numerous IgG biomarkers of acute infection, identified novel IgG biomarkers for acute and chronic infections, and profiled for the first time the IgM antibody repertoire for both acute and chronic Q fever. Using these results we were able to devise a test that can distinguish acute from chronic Q fever. These results also provide a unique perspective on isotype switch and demonstrate the utility of protein microarrays for simultaneously examining the dynamic humoral immune response against thousands of proteins from a large number of patients. The results presented here identify novel seroreactive antigens for the development of recombinant protein-based diagnostics and subunit vaccines, and provide insight into the development of the antibody response.

Evolutionary microbial genomics: insights into bacterial host adaptation

Host-adapted bacteria include mutualists and pathogens of animals, plants and insects. Their study is therefore important for biotechnology, biodiversity and human health. The recent rapid expansion in bacterial genome data has provided insights into the adaptive, diversifying and reductive evolutionary processes that occur during host adaptation. The results have challenged many pre-existing concepts built from studies of laboratory bacterial strains. Furthermore, recent studies have revealed genetic changes associated with transitions from parasitism to mutualism and opened new research avenues to understand the functional reshaping of bacteria as they adapt to growth in the cytoplasm of a eukaryotic host.

Coxiella burnetii expresses a functional Δ24 sterol reductase

Coxiella burnetii, the etiological agent of human Q fever, occupies a unique niche inside the host cell, where it replicates in a modified acidic phagolysosome or parasitophorous vacuole (PV). The PV membrane is cholesterol-rich, and inhibition of host cholesterol metabolism negatively impacts PV biogenesis and pathogen replication. The precise source(s) of PV membrane cholesterol is unknown, as is whether the bacterium actively diverts and/or modifies host cell cholesterol or sterol precursors. C. burnetii lacks enzymes for de novo cholesterol biosynthesis; however, the organism encodes a eukaryote-like Δ24 sterol reductase homolog, CBU1206. Absent in other prokaryotes, this enzyme is predicted to reduce sterol double bonds at carbon 24 in the final step of cholesterol or ergosterol biosynthesis. In the present study, we examined the functional activity of CBU1206. Amino acid alignments revealed the greatest sequence identity (51.7%) with a Δ24 sterol reductase from the soil amoeba Naegleria gruberi. CBU1206 activity was examined by expressing the protein in a Saccharomyces cerevisiae erg4 mutant under the control of a galactose-inducible promoter. Erg4 is a yeast Δ24 sterol reductase responsible for the final reduction step in ergosterol synthesis. Like Erg4-green fluorescent protein (GFP), a CBU1206-GFP fusion protein localized to the yeast endoplasmic reticulum. Heterologous expression of CBU1206 rescued S. cerevisiae erg4 sensitivity to growth in the presence of brefeldin A and cycloheximide and resulted in new synthesis of ergosterol. These data indicate CBU1206 is an active sterol reductase and suggest the enzyme may act on host sterols during C. burnetii intracellular growth.

Actin dynamics and Rho GTPases regulate the size and formation of parasitophorous vacuoles containing Coxiella burnetii

Q fever is a disease caused by Coxiella burnetii. In the host cell, this pathogen generates a large parasitophorous vacuole (PV) with lysosomal characteristics. Here we show that F-actin not only is recruited to but also is involved in the formation of the typical PV. Treatment of infected cells with F-actin-depolymerizing agents alters PV development. The small PVs formed in latrunculin B-treated cells were loaded with transferrin and Lysotracker and labeled with an antibody against cathepsin D, suggesting that latrunculin B did not affect vacuole cargo and its lysosomal characteristics. Nevertheless, the vacuoles were unable to fuse with latex bead phagosomes. It is known that actin dynamics are regulated by the Rho family GTPases. To assess the role of these GTPases in PV formation, infected cells were transfected with pEGFP expressing wild-type and mutant Rac1, Cdc42, and RhoA proteins. Rac1 did not show significant PV association. In contrast, PVs were decorated by both the wild types and constitutively active mutants of Cdc42 and RhoA. This association was inhibited by treatment of infected cells with chloramphenicol, suggesting a role for bacterial protein synthesis in the recruitment of these proteins. Interestingly, a decrease in vacuole size was observed in cells expressing dominant-negative RhoA; however, these small vacuoles accumulated transferrin, Lysotracker, and DQ-BSA. In summary, these results suggest that actin, likely modulated by the GTPases RhoA and Cdc42 and by bacterial proteins, is involved in the formation of the typical PV.

Infection of human monocyte-derived macrophages with Coxiella burnetii

Coxiella burnetii, the agent of Q fever, is an obligate intracellular bacterium that has a tropism for cells of the mononuclear phagocyte system. Following internalization, C. burnetii remains in a phagosome that ultimately matures into a vacuole with lysosomal characteristics that supports pathogen replication. Most in vitro investigations of Coxiella - macrophage interactions have employed continuous cell lines. Although these studies have been informative, genetic alterations of immortalized cells may result in attenuated biological responses to infection relative to primary cells. Consequently, primary macrophages are preferred as in vitro model systems. Here, we describe procedures for propagation and isolation of C. burnetii from cell culture and the use of these preparations to infect primary macrophages derived from human peripheral blood monocytes. Both virulent phase I and avirulent phase II C. burnetii productively infect human monocyte-derived macrophages (MDMs) and replicate with approximately the same kinetics, thereby providing a more physiologically relevant in vitro model system to study the infectious process of this pathogen.

A method for purifying obligate intracellular Coxiella burnetii that employs digitonin lysis of host cells

Purification of the obligate intracellular bacterium Coxiella burnetii requires physical disruption of infected cells. Here we describe a gentle and safe digitonin lysis procedure to release C. burnetii from infected cells. The purity, yield, and infectivity of digitonin-prepped organisms are comparable to that of organisms purified using cell lysis by sonication.

Coxiella burnetii inhibits activation of host cell apoptosis through a mechanism that involves preventing cytochrome c release from mitochondria

Coxiella burnetii is an obligate intracellular pathogen and the etiological agent of the human disease Q fever. C. burnetii infects mammalian cells and then remodels the membrane-bound compartment in which it resides into a unique lysosome-derived organelle that supports bacterial multiplication. To gain insight into the mechanisms by which C. burnetii is able to multiply intracellularly, we examined the ability of host cells to respond to signals that normally induce apoptosis. Our data show that mammalian cells infected with C. burnetii are resistant to apoptosis induced by staurosporine and UV light. C. burnetii infection prevented caspase 3/7 activation and limited fragmentation of the host cell nucleus in response to agonists that induce apoptosis. Inhibition of bacterial protein synthesis reduced the antiapoptotic effect that C. burnetii exerted on infected host cells. Inhibition of apoptosis in C. burnetii-infected cells did not correlate with the degradation of proapoptotic BH3-only proteins involved in activation of the intrinsic cell death pathway; however, cytochrome c release from mitochondria was diminished in cells infected with C. burnetii upon induction of apoptosis. These data indicate that C. burnetii can interfere with the intrinsic cell death pathway during infection by producing proteins that either directly or indirectly prevent release of cytochrome c from mitochondria. It is likely that inhibition of apoptosis by C. burnetii represents an important virulence property that allows this obligate intracellular pathogen to maintain host cell viability despite inducing stress that would normally activate the intrinsic death pathway.

Efficient method of cloning the obligate intracellular bacterium Coxiella burnetii

Coxiella burnetii is an obligate intracellular bacterium that replicates in a large lysosome-like parasitophorous vacuole (PV). Current methods of cloning C. burnetii are laborious and technically demanding. We have developed an alternative cloning method that involves excision of individual C. burnetii-laden PVs from infected cell monolayers by micromanipulation. To demonstrate the cloning utility and efficiency of this procedure, we coinfected Vero cells with isogenic variants of the Nine Mile strain of C. burnetii. Coinhabited PVs harboring Nine Mile phase II (NMII) and Nine Mile phase I (NMI) or Nine Mile crazy (NMC) were demonstrated by immunofluorescence. PVs were then randomly excised from cells coinfected with NMI and NMC by micromanipulation, and PVs harboring both strains were identified by PCR. Fresh Vero cells were subsequently infected with organisms from coinhabited PVs, and the PV excision and PCR screening process was repeated. Without exception, PVs obtained from second-round excisions contained clonal populations of either NMII or NMC, demonstrating that micromanipulation is an efficient and reproducible procedure for obtaining C. burnetii clones.

T cells are essential for bacterial clearance, and gamma interferon, tumor necrosis factor alpha, and B cells are crucial for disease development in Coxiella burnetii infection in mice

Coxiella burnetii, the etiological agent of Q fever, has two phase variants. Phase I has a complete lipopolysaccharide (LPS), is highly virulent, and causes Q fever in humans and pathology in experimental animals. Phase II lacks an LPS O side chain, is avirulent, and does not grow well in immunocompetent animals. To understand the pathogenicity of Q fever, we investigated the roles of immune components in animals infected with Nine Mile phase I (NM I) or Nine Mile phase II (NM II) bacteria. Immunodeficient mice, including SCID mice (deficient in T and B cells), SCIDbg mice (deficient in T, B, and NK cells), nude mice (deficient in T cells), muMT mice (deficient in B cells), bg mice (deficient in NK cells), mice deficient in tumor necrosis factor alpha (TNF-alpha(-/-) mice), and mice deficient in gamma interferon (IFN-gamma(-/-) mice), were compared for their responses to infection. SCID, SCIDbg, nude, and IFN-gamma(-/-) mice showed high susceptibility to NM I, and TNF-alpha(-/-) mice showed modest susceptibility. Disease caused by NM I in SCID, SCIDbg, and nude mice progressed slowly, while disease in IFN-gamma(-/-) and TNF-alpha(-/-) mice advanced rapidly. B- and NK-cell deficiencies did not enhance clinical disease development or alter bacterial clearance but did increase the severity of histopathological changes, particularly in the absence of B cells. Mice infected with NM II showed no apparent clinical disease, but T-cell-deficient mice had histopathological changes. These results suggest that T cells are critical for clearance of C. burnetii, either NM I or NM II, that IFN-gamma and TNF-alpha are essential for the early control of infection, and that B cells are important for the prevention of tissue damage.

Lounging in a lysosome: the intracellular lifestyle of Coxiella burnetii

Most intracellular parasites employ sophisticated mechanisms to direct biogenesis of a vacuolar replicative niche that circumvents default maturation through the endolysosomal cascade. However, this is not the case of the Q fever bacterium, Coxiella burnetii. This hardy, obligate intracellular pathogen has evolved to not only survive, but to thrive, in the harshest of intracellular compartments: the phagolysosome. Following internalization, the nascent Coxiella phagosome ultimately develops into a large and spacious parasitophorous vacuole (PV) that acquires lysosomal characteristics such as acidic pH, acid hydrolases and cationic peptides, defences designed to rid the host of intruders. However, transit of Coxiella to this environment is initially stalled, a process that is apparently modulated by interactions with the autophagic pathway. Coxiella actively participates in biogenesis of its PV by synthesizing proteins that mediate phagosome stalling, autophagic interactions, and development and maintenance of the mature vacuole. Among the potential mechanisms mediating these processes is deployment of a type IV secretion system to deliver effector proteins to the host cytosol. Here we summarize our current understanding of the cellular events that occur during parasitism of host cells by Coxiella.

Shedding routes ofCoxiella burnetiiin dairy cows: implications for detection and control

Reliable detection of Coxiella burnetii shedders is a critical point for the control of the spread of this bacterium among animals and from animals to humans. Coxiella burnetii is shed by ruminants mainly by birth products (placenta, birth fluids), but may also be shed by vaginal mucus, milk, and faeces, urine and semen. However, the informative value of these types of samples to identify shedders under field conditions is unknown. Our aim was then to describe the responses obtained using a real-time PCR technique applied to milk, vaginal mucus and faeces samples taken from 242 dairy cows in commercial dairy herds known to be naturally infected with Coxiella burnetii, and to assess their putative associations. Positive results were found in all types of tested samples even in faeces. No predominant shedding route was identified. Among the shedder cows, 65.4% were detected as shedders by only one route. By contrast, cows with positive results for all three samples were scarce (less than 7%). Testing a cow based on only one type of biological sample may lead to misclassify it with regards to its shedding of Coxiella burnetii and thereby underestimate the risk of bacterial spread within a herd.

New criteria for immunofluorescence assay for Q fever diagnosis in Japan

A study was made to evaluate the cutoff value of indirect immunofluorescent-antibody (IFA) test for Q fever diagnosis in Japan. We used 346 sera, including 16 from confirmed Q fever cases, 304 from Japanese pneumonia patients, and 26 from negative cases. Thirteen sera from the confirmed Q fever cases with an immunoglobulin M (IgM) titer of > or =1:128 and/or IgG titer of > or =1:256 by the IFA test were positive by both enzyme-linked immunosorbent assay (ELISA) and Western blotting assay (WBA), whereas 298 sera from pneumonia patients and 26 negative sera with an IgM titer of < or =1:16 and an IgG titer of < or =1:32 by the IFA test were negative by both ELISA and WBA. In the proposed "equivocal area," with an IgM titer of > or =1:32 and < or =1:64 and/or an IgG titer of > or =1:64 and < or =1:128, we found 9 sera, 3 from confirmed Q fever cases and 6 from Japanese pneumonia patients, by the IFA test. Three sera from the confirmed Q fever cases and one of the sera from pneumonia patients were IgM and/or IgG positive by both ELISA and WBA. These results suggest that a single cutoff value for the IFA test may cause false-positive and false-negative results. In conclusion, this study showed that an "equivocal area" should be used for the IFA test rather than a single cutoff value and that sera in the equivocal area should be tested by additional serological assays for confirmation.

Natural history and pathophysiology of Q fever

Q fever is a zoonosis caused by Coxiella burnetii. Infection with C burnetii can be acute or chronic, and exhibits a wide spectrum of clinical manifestations. The extreme infectivity of the bacterium results in large outbreaks and makes it a potential bioweapon. In the past decade, the complete genome sequencing of C burnetii, the exploration of bacterial interactions with the host, and the description of the natural history of the disease in human beings and in experimental models have all added to our knowledge about this fascinating disease. Advances in understanding the pathophysiology and natural history of Q fever are reviewed.

Identification and characterization of an immunodominant 28-kilodalton Coxiella burnetii outer membrane protein specific to isolates associated with acute disease

Coxiella burnetii causes acute Q fever in humans and occasional chronic infections that typically manifest as endocarditis or hepatitis. Isolates associated with acute disease were found to be distinct from a group of chronic disease isolates by a variety of biochemical parameters and in a guinea pig fever model of acute disease, suggesting a difference in virulence potential. We compared antigenic polypeptides among C. burnetii isolates and found an immunodominant 28-kDa protein in acute group isolates but not in chronic group isolates (T. Ho, A. Hotta, G. Q. Zhang, S. V. Nguyen, M. Ogawa, T. Yamaguchi, H. Fukushi, and K. Hirai, Microbiol. Immunol. 42:81-85, 1998). In order to clone the adaA gene, the N-terminal amino acid sequence of adaA was determined and a 59-bp fragment was amplified from Nine Mile phase I DNA by PCR. The putative gene fragment was used to screen a lambda ZAP II genomic DNA library, and an open reading frame expressing a 28-kDa immunoreactive protein was identified. Sequence analysis predicted a gene encoding an approximately 28-kDa mature protein with a typical signal sequence. The adaA (acute disease antigen A) gene was detected in acute group C. burnetii isolates but not identified in chronic group isolates by PCR and Southern blotting. A typical signal peptide was predicted in adaA, and specific antibody to adaA reacted with the purified membrane fraction of acute group isolates by Western blotting, suggesting that adaA is exposed on the outer surface of C. burnetii. adaA was overexpressed in pET23a as a fusion protein in Escherichia coli to develop anti-recombinant adaA (anti-radaA) specific antibody, which recognized a approximately 28-kDa band in acute group isolates but not in chronic group isolates. In addition, immunoblotting indicates that radaA reacted with sera derived from animals infected with acute group isolates but did not react with sera from animals infected with chronic group isolates. These results support the idea that an adaA gene-targeted PCR assay and an radaA antigen-based serodiagnostic test may be useful for differential diagnosis of acute and chronic Q fever.

Risk of Occupationally Acquired Illnesses from Biological Threat Agents in Unvaccinated Laboratory Workers

Many vaccines for bioterrorism agents are investigational and therefore not available (outside of research protocol use) to all at-risk laboratory workers who have begun working with these agents as a result of increased interest in biodefense research. Illness surveillance data archived from the U.S. offensive biological warfare program (from 1943 to 1969) were reviewed to assess the impact of safety measures on disease prevention (including biosafety cabinets [BSCs]) before and after vaccine availability. Most laboratory-acquired infections from agents with higher infective doses (e.g., anthrax, glanders, and plague) were prevented with personal protective measures and safety training alone. Safety measures (including BSCs) without vaccination failed to sufficiently prevent illness from agents with lower infective doses in this high-risk research setting. Infections continued with tularemia (average 15/year), Venezuelan equine encephalitis (1.9/year), and Q fever (3.4/year) but decreased dramatically once vaccinations became available (average of 1, 0.6, and 0 infections per year, respectively). While laboratory-acquired infections are not expected to occur frequently in the current lower-risk biodefense research setting because of further improvements in biosafety equipment and changes in biosafety policies, the data help to define the inherent risks of working with the specific agents of bioterrorism. The data support the idea that research with these agents should be restricted to laboratories with experience in handling highly hazardous agents and where appropriate safety training and precautions can be implemented.

Stimulation of toll-like receptor 2 by Coxiella burnetii is required for macrophage production of pro-inflammatory cytokines and resistance to infection

Innate and adaptive immune responses are initiated upon recognition of microbial molecules by Toll-like receptors (TLRs). We have investigated the importance of these receptors in the induction of pro-inflammatory cytokines and macrophage resistance to infection with Coxiella burnetii, an obligate intracellular bacterium and the etiological agent of Q fever. By using a Chinese hamster ovary/CD14 cell line expressing either functional TLR2 or TLR4, we determined that C. burnetii phase II activates TLR2 but not TLR4. Macrophages deficient for TLR2, but not TLR4, produced less tumor necrosis factor-alpha and interleukin-12 upon C. burnetii infection. Furthermore, it was found that TLR2 activation interfered with C. burnetii intracellular replication, as macrophages from TLR2-deficient mice were highly permissive for C. burnetii growth compared with macrophages from wild type mice or TLR4-deficient mice. Although LPS modifications distinguish virulent C. burnetii phase I bacteria from avirulent phase II organisms, electrospray ionization-mass spectrometry analysis showed that the lipid A moieties isolated from these two phase variants are identical. Purified lipid A derived from either phase I or phase II LPS failed to activate TLR2 and TLR4. Indeed, the lipid A molecules were able to interfere with TLR4 signaling in response to purified Escherichia coli LPS. These studies indicate that TLR2 is an important host determinant that mediates recognition of C. burnetii and a response that limits growth of this intracellular pathogen.

Phagocytosis of apoptotic cells increases the susceptibility of macrophages to infection with Coxiella burnetii phase II through down-modulation of nitric oxide production

Coxiella burnetii, the agent of Q fever in humans and coxiellosis in other mammals, is an obligate intracellular bacterium which is sheltered and multiplies within typically large phagolysosome-like replicative vacuoles (LRVs). We have previously shown that, compared with fibroblasts, mouse resident peritoneal macrophages control the development of LRVs and bacterial multiplication within these vacuoles. Earlier experiments with the nitric oxide (NO) synthase inhibitor aminoguanidine (AG) revealed that the control is exerted by NO induced by the bacteria. We report here that phagocytosis of apoptotic-like, but not of aldehyde-killed, lymphocytes by the macrophages reduced the production of NO induced by the bacteria and increased the development of LRVs and, therefore, the total bacterial load in the cultures. Experiments with macrophages from mice deficient for inducible NO synthase (iNOS(-)/(-)) confirmed the involvement of NO in the control of infection, since neither apoptotic lymphocytes nor AG affected the development of LRVs in these phagocytes. Since macrophages are important for the clearance of apoptotic bodies and C. burnetii is able to induce apoptosis in human monocytes, the phenomenon shown here may be biologically relevant to the development of Q fever and coxiellosis.

Identification and cloning of immunodominant antigens of Coxiella burnetii

A sublethal-challenge model was established in BALB/c mice by using protection from the development of severe splenomegaly as an indicator of vaccinogenic activity for evaluation of the protective efficacies of vaccine candidates. To determine the immunodominant antigens as defined by reaction to an infection-derived antibody, mouse sera from different stages of experimental infection with various doses of Coxiella burnetii were tested by immunoblotting. Proteins with molecular masses of 14, 16, 21, 28, 32, 45 to 50, 57, and 60 kDa were recognized as immunodominant antigens. Antibody responses in whole-cell antigen (WCA)-vaccinated mice were compared with those in unvaccinated mice by immunoblotting using two-dimensional gel-separated C. burnetii antigens. The results indicated that there were significantly different antibody responses during different stages of vaccination and challenge, suggesting that several specific immunogenic antigens may play critical roles in the protection of mice against challenge. To clone these immunogenic antigens, a genomic DNA library of Nine Mile phase I was screened with convalescent-phase antisera from mice. Eighteen novel immunoreactive proteins with molecular masses ranging from approximately 14 to 67 kDa were cloned and identified. Interestingly, several recombinant proteins reacted with sera from both early-stage infected and WCA-vaccinated prechallenged mice. These results suggest that these proteins may play critical roles in the development of protective immunity and that they are logical candidates for vaccine and serodiagnostic reagents.